In hydrocarbon wells, tools incorporating valve assemblies having a restrictor element, such as a ball or dart, and a seat element, such as a ball seat or dart seat, have been used for a number of different operations. Such valve assemblies prevent the flow of fluid past the assembly and, with the application of a desired pressure, can actuate one or more tools associated with the assembly.
One use for such remotely operated valve assemblies is in fracturing (or “fracing”), a technique used by well operators to create and/or extend one or more cracks, called “fractures” from the wellbore deeper into the surrounding formation in order to improve the flow of formation fluids into the wellbore. Fracing is typically accomplished by injecting fluids from the surface, through the wellbore, and into the formation at high pressure to create the fractures and to force them to both open wider and to extend further. In many case, the injected fluids contain a granular material, such as sand, which functions to hold the fracture open after the fluid pressure is reduced.
Multiple valve assemblies which incorporate ball-and-seat seals, each having a differently-sized ball seat and corresponding ball, are known in the art. Frac valves connected to ball and seat valve do not require the running of a shifting tool thousands of feet into the tubing string and are simpler to actuate than frac valves requiring such shifting tools. Such ball and seat valves are operated by placing an appropriately sized ball into the well bore and bringing the ball into contact with a corresponding ball seat. The ball engages on a sealing section of the ball seat to block the flow of fluids past the valve assembly. Application of pressure to the valve assembly causes the valve assembly to “shift”, opening the frac sleeve.
Some valve assemblies are selected for tool actuation by the size of ball or other restrictor element introduced into the well. If the well or tubing string contains multiple ball seats, the ball must be small enough that it will not seal against any of the ball seats it encounters prior to reaching the desired ball seat. For this reason, the smallest ball to be used for the planned operation is the first ball placed into the well or tubing and the smallest ball seat is positioned in the well or tubing the furthest from the wellhead. The balls in such ball and seat valves are often free to travel back up the tubing (e.g. back toward the point in which the ball is inserted into the well) when pressure on the downstream side of the ball exceeds the pressure on the upstream side of the ball. Thus, these traditional valve assemblies limit the number of valves that can be used in a given tubing string because each ball size is only able to actuate a single valve. This arrangement allows for each ball to travel from the insertion point to its desired seat and then to be removed from the well by fluid flowing from the well back to the surface.
The described embodiments and invention as claimed relate to a downhole tool that can capture a ball in a trap to prevent both upwell and downwell movement of the ball. Further, certain embodiments described herein may prevent fluid from flowing past a captured in either the upwell or downwell directions. Ball and seat valves incorporating such ball trap assemblies can be used to create a bi-directional plug which prevents fluid flow in either direction when the ball trap is engaged with an appropriately configured ball.